The 3-(substituted oxy)-4-pyridazinol derivative in the present invention is useful as medicines, agricultural chemicals, functional materials, or intermediates thereof. For example, 3-phenoxy-4-pyridazinol derivatives are known to have a herbicidal activity (patent document 1). Further, ester derivatives of 3-phenoxy-4-pyridazinol compounds are known to have a similar herbicidal activity (patent document 1). As an example of the compounds, 3-phenoxy-4-pyridazinyl 4-morpholinecarboxylate is described (patent document 1).
As methods for producing the pyridazinol derivative in the present invention, patent document 1 shows the following methods.
1) A method for producing a 6-chloro-3-phenoxy-4-pyridazinol derivative, which comprises reacting 3,6-dichloropyridazine with phenols to obtain a 3-chloro-6-phenoxy derivative, and then subjecting the pyridazine ring in the derivative to chlorination to obtain a 3,5-dichloro-6-phenoxypyridazine derivative, and hydrolyzing the obtained derivative to produce a 6-chloro-3-phenoxy-4-pyridazinol derivative. However, this method has reactions of three steps and has low selectivity in the chlorination, and cannot be a satisfying production method.
2) A method for producing a 3-phenoxy-4-pyridazinol derivative, which comprises oxidizing 3,6-dichloropyridazine using an oxidizing agent to provide 3,6-dichloropyridazine-1-oxide, and reacting the resultant oxide with a phenol derivative to obtain 6-chloro-3-phenoxypyridazine-1-oxide, and then subjecting the obtained compound to chlorination using phosphorus oxychloride to obtain a 3,5-dichloro-6-phenoxypyridazine derivative, and hydrolyzing the obtained derivative to produce a 3-phenoxy-4-pyridazinol derivative. However, this method has reactions of four steps and cannot be a satisfying production method.
3) A method for producing a 3-phenoxy-4-pyridazinol derivative, which comprises reacting 3,6-dichloropyridazine with phenols to obtain a 3-chloro-6-phenoxypyridazine derivative, and then oxidizing the obtained derivative using an oxidizing agent to obtain 6-chloro-3-phenoxypyridazin-1-oxide, and subsequently, subjecting the obtained compound to chlorination using phosphorus oxychloride to obtain a 3,5-dichloro-6-phenoxypyridazine derivative, and hydrolyzing the obtained derivative to produce a 3-phenoxy-4-pyridazinol derivative. However, this method has reactions of four steps and cannot be a satisfying production method.
4) A method for producing a 3-phenoxy-4-pyridazinol derivative, which comprises reacting 3,6-dichloro-4-methoxypyridazine with phenols to obtain a 3-phenoxy-4-methoxypyridazine derivative, and hydrolyzing the obtained derivative to produce a 3-phenoxy-4-pyridazinol derivative. In this method, however, a 3-phenoxy-5-methoxypyridazine derivative is produced as a main product in the first step, so that the yield of the 3-phenoxy-4-methoxypyridazine derivative which is a desired product is reduced, and thus this method cannot be a satisfying production method.
5) A method for producing a 6-chloro-3-phenoxy-4-pyridazinol derivative, which comprises reacting 3,6-dichloropyridazine with phenols to obtain a 3-chloro-6-phenoxypyridazine derivative, and then replacing the chlorine atom in the obtained derivative by a hydrogen atom using a reducing agent to obtain a 3-phenoxypyridazine derivative, and then oxidizing the obtained derivative using an oxidizing agent to obtain 3-phenoxypyridazin-1-oxide, and reacting the obtained compound with a metalation agent to effect metalation of the pyridazine ring at 6-position, and then reacting the resultant compound with an electrophile to introduce a chloro substituent or the like to the 6-position of the pyridazine ring, and subsequently, subjecting the resultant compound to chlorination using phosphorus oxychloride to obtain a 4,6-dichloro-3-phenoxypyridazine derivative, and hydrolyzing the obtained derivative to produce a 6-chloro-3-phenoxy-4-pyridazinol derivative. However, this method has reactions of seven steps and cannot be a satisfying production method.
6) A method for producing a 3-(2-hydroxyphenoxy)-4-pyridazinol derivative, which comprises reacting 3,4,6-trichloropyridazine with catechols, and then hydrolyzing the resultant 3-chloro[1,4]benzodioxino[2,3-c]pyridazine derivative to produce a 3-(2-hydroxyphenoxy)-4-pyridazinol derivative. However, this method has reactions of two steps, and further the derivative obtained by the method is limited to a 2-hydroxyphenoxy derivative, and this method cannot be a satisfying production method.
Further, patent document 1 has a description about a method for producing a 3-phenoxy-4-hydroxypyridazine derivative, which comprises reacting 4-hydroxypyridazine with phenols. However, this method is merely formally described and no specific example of the method is shown.    Patent document 1: Japanese Unexamined Patent Publication No. 2004-2263